Nickel Based Alloy with High Fatigue Resistance and Methods of Forming the Same

ABSTRACT

A nickel based alloy, along with methods of its use and manufacture, is provided that may include about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; and the balance nickel. The nickel based alloy may have gamma prime precipitates in a plurality of grain interiors and a gamma prime solvus temperature of about 1038° C. or greater. Additionally or alternatively, the nickel based alloy may comprise about 30% by volume or more gamma prime precipitates in the plurality of grain interiors.

FIELD

The subject matter disclosed herein relates generally to high temperature alloys. More particularly, embodiments of the present invention generally relate to nickel based alloys, along with articles formed from nickel based alloys and methods of forming the same.

BACKGROUND

Generally, gas turbine engines include a compressor, combustor, and a turbine. The compressor compresses air and includes a series of stages of blades rotating around a shaft. The compressed air is mixed with a fuel and channeled to the combustor, where the mixture is ignited within a combustion chamber to generate hot combustion gases. The combustion gases are channeled to the turbine. The turbine section contains a rotor shaft and one or more turbine stages, each having a turbine disk (or rotor) mounted or otherwise carried by the shaft and turbine blades mounted to and radially extending from the periphery of the disk. A turbine assembly typically generates rotating shaft power by expanding hot compressed gas produced by the combustion of a fuel. Gas turbine buckets or blades generally have an airfoil shape designed to convert the thermal and kinetic energy of the flow path gases into mechanical rotation of the rotor.

The components of a gas turbine engine, particularly the components of the combustor or high pressure turbine, are exposed to high operating temperatures. Accordingly, materials for the production of such components are needed that can withstand high operating temperatures while maintaining mechanical strength. The capabilities of these materials impact the efficiency of the engine both in the present and overtime. Further, next generation gas turbine engines need higher temperature capabilities to achieve high cycle efficiencies, such as about 65% combined cycle efficiency or more.

As such, an improved alloy with higher temperature strength, creep resistance, fatigue resistance, and environmental resistance without sacrificing processibility, ductility, and fatigue crack growth resistance is desirable in the art.

BRIEF DESCRIPTION

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

A nickel based alloy is generally provided, along with methods of its use and manufacture. In one embodiment, the nickel based alloy comprises about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; and the balance nickel. For example, in one particular embodiment, the nickel based alloy comprises about 22% by weight to about 24% by weight cobalt, about 10% by weight to about 12% by weight chromium, about 3% by weight to about 5% by weight iron, about 4% by weight to about 5.5% by weight aluminum, about 10% by weight to about 12% by weight tungsten, about 7% by weight to about 8% by weight tantalum, and about 0.07% by weight to about 0.15% by weight boron.

In certain embodiments, the nickel based alloy comprises gamma prime precipitates in a plurality of grain interiors and has a gamma prime solvus temperature of about 1038° C. or greater. Additionally or alternatively, the nickel based alloy may comprise about 30% by volume or more gamma prime precipitates in the plurality of grain interiors (e.g., about 20% by volume or more).

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended FIGS., in which:

FIG. 1a shows a back-scattered electron SEM image of Alloy 1 according to Example 1;

FIG. 1b shows an enlarged back-scattered electron SEM image of Alloy 1 according to Example 1;

FIG. 2a shows a back-scattered electron SEM image of Alloy 2 according to Example 1;

FIG. 2b shows an enlarged back-scattered electron SEM image of Alloy 2 according to Example 1;

FIG. 3a shows a back-scattered electron SEM image of Alloy 4 according to Example 1;

FIG. 3b shows an enlarged back-scattered electron SEM image of Alloy 4 according to Example 1;

FIG. 4a shows a back-scattered electron SEM image of Alloy 6 according to Example 1;

FIG. 4b shows an enlarged back-scattered electron SEM image of Alloy 6 according to Example 1;

FIG. 5a shows the grain boundary phase fraction of some of the alloys of Example 1;

FIG. 5b shows the grain boundary phase lineal density of some of the alloys of Example 1;

FIG. 6a shows the tensile properties, in terms of 0.2% yield strength, of the alloys 1-6 of Example 1 compared to Haynes® Alloy 282 (“HA282”);

FIG. 6b shows the tensile properties, in terms of elongation, of the alloys 1-6 of Example 1 compared to Haynes® Alloy 282 (“HA282”);

FIG. 7 shows the creep rupture properties of Alloys 1, 2, 4, 5, and 6 of Example 1 plotted as the Larson-Miller parameter (LMP) as a function of stress compared to HA282;

FIG. 8a shows the hold time low cycle fatigue (“LCF”) at 1700° F. (i.e. about 927° C.) at a strain range of 0.35% of the Alloys 1-6 of Example 1 compared to HA282;

FIG. 8b shows the hold time low cycle fatigue (“LCF”) at 1700° F. (i.e. about 927° C.) at a strain range of 0.5% of the Alloys 3, 4, 5, and 6 of Example 1 compared to HA282;

FIG. 9 shows the fracture toughness (K_(1C)) of Alloys 1, 2, 3, 5, and 6 of Example 1 compared to HA282, as measured at 1700° F. (i.e., about 927° C.);

FIG. 10 shows results of a cyclic oxidation test comparing Alloy 6 of Example 1 to HA282 at 1800° F. (i.e., about 982° C.) with cycles of 50 minutes in the furnace at 1800° F. and 10 minutes out of the furnace;

FIG. 11a shows a back-scattered electron SEM image of Alloy A according to Example 2;

FIG. 11b shows a back-scattered electron SEM image of Alloy B according to Example 2;

FIG. 11c shows a back-scattered electron SEM image of Alloy C according to Example 2;

FIG. 11d shows a back-scattered electron SEM image of Alloy D according to Example 2;

FIG. 11e shows a back-scattered electron SEM image of Alloy E according to Example 2;

FIG. 11f shows a back-scattered electron SEM image of Alloy F according to Example 2;

FIG. 12a shows the grain boundary phase fraction of the alloys of Example 2; and

FIG. 12b shows the grain boundary phase lineal density of the alloys of Example 2.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and is not a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

In the present disclosure, when a layer is being described as “on” or “over” another layer or substrate, it is to be understood that the layers can either be directly contacting each other or have another layer or feature between the layers, unless expressly stated to the contrary. Thus, these terms are simply describing the relative position of the layers to each other and do not necessarily mean “on top of” since the relative position above or below depends upon the orientation of the device to the viewer.

Chemical elements are discussed in the present disclosure using their common chemical abbreviation, such as commonly found on a periodic table of elements. For example, hydrogen is represented by its common chemical abbreviation H; helium is represented by its common chemical abbreviation He; and so forth.

As used herein, “substantially” refers to at least about 90% or more of the described group. For instance, as used herein, “substantially all” indicates that at least about 90% or more of the respective group have the applicable trait and “substantially no” or “substantially none” indicates that at least about 90% or more of the respective group do not have the applicable trait. As used herein, the “majority” refers to at least about 50% or more of the described group. For instance, as used herein, “the majority of” indicates that at least about 50% or more of the respective group have the applicable trait.

The compositional ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 wt. %”, or, more specifically, “about 5 wt. % to about 20 wt. %”, are inclusive of the endpoints and all intermediate values of the ranges). Weight levels are provided on the basis of the weight of the entire composition, unless otherwise specified; and ratios are also provided on a weight basis. Moreover, the term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The modifier “about” used in connection with a quantity is inclusive of the stated value, and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., “the refractory element(s)” may include one or more refractory elements). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described inventive features may be combined in any suitable manner in the various embodiments.

Nickel based alloys are generally provided herein, along with methods of forming such an alloy and articles comprising such an alloy. Components formed from such nickel based alloys may be used at higher operating temperatures than currently available commercial alloys. The nickel based alloy contains various elements, such as cobalt (Co), chromium (Cr), iron (Fe), aluminum (Al), tungsten (W), tantalum (Ta), boron (B), and nickel (Ni). Optionally, the nickel based alloy may also contain other elements, such as carbon (C), hafnium (Hf), zirconium (Zr), or a mixture thereof. Generally, the nickel based alloy is processible into sheet form from cast ingots through wrought processes. The nickel based alloy generally possesses superior high temperature properties, including hold time low cycle fatigue (LCF), tensile properties, creep, and oxidation resistance, compared with other commercially available high temperature wrought alloys, such as Haynes® Alloy 282 (“HA282”), while maintaining acceptable ductility and fatigue crack growth properties.

Generally, the nickel based alloy possesses unique microstructural features. In certain embodiments, the nickel based alloy is strengthened by gamma-prime precipitates (e.g., gamma-prime Ni₃Al precipitates) in the grain interiors and/or W-bearing precipitates (e.g., Co₂W Laves phase, mu-phase, boride phases, carbide phases) along the grain boundaries. Without intending to be limited by theory, it is believed that the gamma-prime precipitates may contribute to the yield strength, to the ultimate tensile strength and to the creep resistance, all of which are generally higher than prior alloys. In certain embodiments, creep life may be about three (3) times that of prior alloys. Furthermore, it is believed that the grain boundary precipitates of W-bearing phases may contribute to ductility and fatigue resistance. The nickel based alloy may have superior hold time LCF resistance compared with prior alloys, due, at least in part, to the combination of the superior creep resistance by gamma-prime precipitates and the grain boundaries strengthened by the precipitation of the Laves phase and other W-bearing phases. Fatigue crack growth threshold and fracture toughness of the nickel based alloy are acceptable for various applications, such as use in gas turbine combustors. In certain embodiments, without the precipitation of the Laves phase and other W-bearing phases along the grain boundaries, the ductility, hold time LCF life, and fracture toughness may become inferior. In some embodiment, the alloy may also contain a small amount of sigma phase and/or beta phases, of which may not harm the properties of the alloy.

The nickel based alloy may contain sufficient aluminum for alumina formation during oxidation and may show far less weight gain or loss during cyclic oxidation compared to prior alloys. The nickel based alloy can be processed into sheet form by hot rolling and is weldable without cracking. In one embodiment, the nickel based alloy may be subjected to solution heat treatment and/or aging treatment. For example, solution heat treatment may be performed by heating the nickel based alloy to a solution temperature that is between its solidus temperature and its gamma prime solvus temperature. The aging treatment may be performed by heating the nickel based alloy to an aging temperature that is below the gamma prime solvus temperature.

In particular embodiments, the nickel based alloy comprises about 30% by volume or more of gamma prime precipitates in the grain interiors. Excluding super fine gamma prime precipitates formed during cooling after aging treatment the nickel base alloy can have about 30% to about 60% by volume gamma prime precipitates in the grain interiors, about 35% to about 55% by volume gamma prime precipitates in the grain interiors. In certain embodiments, the nickel base alloy has gamma prime solvus temperature about 1900° F. (1038° C.) or greater.

In certain embodiments, the nickel based alloy has a grain boundary fraction of W-bearing phases about 20% by volume or more, preferably about 25% or more. Additionally, the nickel based alloy has a grain boundary phase lineal density of about 310 precipitates per mm or greater.

In one particular embodiment, the nickel based alloy comprises discrete and fine refractory element bearing precipitates along one or more grain boundaries, such as Laves phase precipitates, mu phase precipitates, sigma phase precipitates, beta phase precipitates, boride phase precipitates, carbide phase precipitates, or mixtures thereof. In one particular embodiment, for instance, the nickel based alloy comprises Laves phase precipitates along one or more grain boundaries. For example, the Laves phase precipitates may be W-bearing precipitates, and may include some mu phase therein/therewith.

As stated, the nickel based alloy may comprise the following elements: nickel, cobalt, chromium, iron, aluminum, tungsten, tantalum, boron, and optionally one or more of carbon, hafnium, and zirconium. Each of these elements is included in a particular concentration such that the resulting nickel based alloy has the desired properties, as discussed above. In certain embodiments, the nickel based alloy comprises: about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; and the balance nickel. Optional components may also be included in such a nickel based alloy, such as up to about 0.1% by weight carbon (e.g., greater than 0% by weight to about 0.1% carbon, preferably about 0.02% by weight to about 0.08% by weight carbon), up to about 0.5% by weight hafnium (e.g., greater than 0% by weight to about 0.5% by weight hafnium), and/or up to about 0.1% by weight zirconium (e.g., greater than 0% by weight to about 0.1% by weight zirconium).

Without wishing to be bound by any particular theory, within the composition spaces investigated (see e.g., examples 1 and 2 discussed below), it is believed that the relatively high concentrations of iron and boron, combined with the relatively low concentrations of cobalt, leads to the desired properties. In particular, it is believed that the increased amount of iron and boron and the decreased amount of cobalt, leads to the desired microstructure that includes the gamma prime precipitates (e.g., at about 30% by volume or more of gamma prime precipitates in the grain interiors, as described above), the grain boundary phase fraction (e.g., of about 20% by volume or more of the grain boundary phase fraction), and/or the grain boundary phase lineal density (e.g., of about 310 precipitates per mm or greater of the grain boundary phase lineal density.

In more preferred embodiments, the nickel based alloy comprises: about 22 wt. % to about 24 wt. % cobalt; about 10 wt. % to about 12 wt. % chromium; about 3 wt. % to about 5 wt. % iron; about 4.0 wt. % to about 5.5 wt. % aluminum; about 10 wt. % to about 12 wt. % tungsten; about 7 wt. % to about 8 wt. % tantalum; about 0.07 wt. % to about 0.15 wt. % boron; up to about 0.1% by weight carbon (e.g., greater than 0% by weight to about 0.1% carbon, preferably about 0.02% by weight to about 0.08% by weight carbon); up to about 0.5% by weight hafnium (e.g., greater than 0% by weight to about 0.5% by weight hafnium); and/or up to about 0.1% by weight zirconium (e.g., greater than 0% by weight to about 0.1% by weight zirconium); with the balance being nickel.

The concentrations of each of these elements may be summarized, as shown in Table 1, with all values given in percent by weight (% wt.). It is to be understood that the ranges from the preferred ranges and the more preferred ranges may be combined as desired.

TABLE 1 Element Preferred Range (% wt.) More Preferred (% wt.) Co about 20 to about 26 about 22 to about 24 Cr about 9 to about 13 about 10 to about 12 Fe about 2 to about 6 about 3 to about 5 Al about 3.5 to about 6 about 4 to about 5.5 W about 9 to about 13 about 10 to about 12 Ta about 6 to about 9 about 7 to about 8 B about 0.06 to about 0.20 about 0.07 to about 0.15 C 0 to about 0.10 about 0.02 to about 0.08 Hf 0 to about 0.50 greater than 0 to about 0.50 Zr 0 to about 0.10 greater than 0 to about 0.10 Ni Balance Balance

Those skilled in the art understand that minor trace amounts of other elements at impurity levels are inevitably present, e.g., in commercially-supplied alloys, or by way of processing techniques. Those impurity-level additions may also be considered as part of the nickel based alloy, as long as they do not detract from the properties of the compositions described herein. As such, in certain embodiments, the nickel based alloy may consist essentially of: about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; up to about 0.1% by weight carbon (e.g., greater than 0% by weight to about 0.1% carbon, preferably about 0.02% by weight to about 0.08% by weight carbon), up to about 0.5% by weight hafnium (e.g., greater than 0% by weight to about 0.5% by weight hafnium), up to about 0.1% by weight zirconium (e.g., greater than 0% by weight to about 0.1% by weight zirconium), and the balance nickel.

For instance, in a preferred embodiment, the nickel based alloy may consist essentially of: about 22 wt. % to about 24 wt. % cobalt; about 10 wt. % to about 12 wt. % chromium; about 3 wt. % to about 5 wt. % iron; about 4.0 wt. % to about 5.5 wt. % aluminum; about 10 wt. % to about 12 wt. % tungsten; about 7 wt. % to about 8 wt. % tantalum; about 0.07 wt. % to about 0.15 wt. % boron; up to about 0.1% by weight carbon (e.g., greater than 0% by weight to about 0.1% carbon, preferably about 0.02% by weight to about 0.08% by weight carbon); up to about 0.5% by weight hafnium (e.g., greater than 0% by weight to about 0.5% by weight hafnium); and/or up to about 0.1% by weight zirconium (e.g., greater than 0% by weight to about 0.1% by weight zirconium); with the balance being nickel.

The presently disclosed nickel based alloys may be used to prepare a variety of components, and are particularly suitable for use in high temperature applications. For instance, the nickel based alloy may be used to prepare components for use in turbomachinery, such as with aviation engines (e.g., turbofan, turbojet, turboprop and turboshaft gas turbine engines), industrial engines, marine engines, and auxiliary power units. In particular embodiments, the nickel based alloys may be used to prepare components for gas turbine engines, such as in high pressure compressors (HPC), fans, boosters, high pressure turbines (HPT), low pressure turbines (LPT), turbine cases, and combustors of both airborne and land-based gas turbine engines. For instance, components such as combustion liners, shrouds, nozzles, blades, etc. may be prepared with the present method and materials.

Methods are also generally provided for forming a nickel based alloy and for articles formed form the nickel based alloy. The nickel based alloys may be prepared by way of any of the various traditional methods of metal production and forming. For instance, the nickel based alloy may be prepared by traditional wrought alloy techniques, traditional casting, powder metallurgical processing, directional solidification, single-crystal solidification, additive manufacturing, and combinations thereof. Thermal and thermo-mechanical processing and cold/warm working and forming techniques common in the art for the formation of other alloys may be suitable for use in manufacturing and strengthening the nickel based alloy. The article comprising the nickel based alloy may be prepared by a variety of forging and machining techniques to shape and cut articles formed from the alloy composition. In some embodiments, the nickel based alloy can be formed into a pre-determined shape, and then subjected to a solution treatment, followed by an aging treatment.

The nickel based alloy can be formed into many shapes and articles, e.g., plates, bars, wire, rods, sheets, and the like. The article may be a shape or form that allows for transportation of the alloy from one customer to another. The nickel based alloy is particularly suitable for high temperature articles. Examples include various parts for aeronautical turbines, land-based turbines, and marine turbines. For instance, the nickel based alloy may be used to prepare turbine components, such as vanes, blades, stators, and combustor components, such as combustor liners and transition pieces. However, the nickel based alloy is not limited to such components or uses.

The nickel based alloy can be used to protect other articles or alloy structures. For instance, a layer comprising the nickel based alloy can be attached, deposited or otherwise formed on another alloy structure or part which requires properties characteristic of the nickel based alloy, e.g., environmental resistance and high temperature strength. (The underlying substrate could be formed of a variety of metals and metal alloys, e.g., iron, steel alloys, or other nickel- or cobalt-alloys). The overall product could be considered a composite structure, or a coating, or an “alloy cladding” over a base metal or base metal core. Bonding of the cladding layer to the underlying substrate could be carried out by conventional methods, such as diffusion bonding, hot isostatic pressing, or brazing. Moreover, those skilled in the art would be able to select the most appropriate thickness of the cladding layer, for a given end use, based in part on the teachings herein.

The examples presented below are intended to be merely illustrative, and should not be construed to be any sort of limitation on the scope of the claimed invention. Sub-scale heats were produced to screen mechanical and environmental resistance of the alloy as well as hot roll possibility and weldability.

Example 1

The nickel based alloy compositions shown in Table 2 were prepared, with all values shown in percent by weight (% wt.). Gamma prime solvus temperatures were measured by differential scanning calorimetry:

TABLE 2 Exemplary Alloy Compositions Gamma prime wt % solvus temperature Alloy Co Cr Fe Al W Ta B C Hf Zr Ni (° C.) 1 31.4 10.9 0.0 5.0 9.8 6.8 0.020 0.05 0.27 0.06 Balance 1107 2 27.0 10.9 3.9 4.6 10.7 7.6 0.022 0.05 0.23 0.06 Balance 1078 3 23.4 11.1 4.1 4.8 10.7 7.4 0.016 0.05 0.17 0.05 Balance 1099 4 23.4 10.8 3.9 4.7 11.0 7.3 0.029 0.05 0.18 0.05 Balance 1099 5 23.8 11.1 4.2 4.8 10.6 7.3 0.044 0.06 0.17 0.01 Balance 1090 6 23.0 10.9 4.0 4.8 11.5 7.6 0.125 0.05 0.23 0.07 Balance 1089

Each of these nickel based alloys was cast by vacuum induction melting, and formed into sheet by hot rolling, and their respective microstructures were compared after solution heat treatment and aging treatment. The solution was done at a temperature between the solidus and the gamma prime solvus temperatures, and aging treatment was done at a temperature below the gamma prime solvus temperature. As discussed in greater detail below, Alloy 6 was exhibited the most desired combination of properties, particularly the high concentration of fine, discrete W-bearing precipitates along the grain boundaries and the relatively high concentration of gamma prime precipitates in the grain interiors.

FIGS. 1a and 1b show back-scattered electron SEM images of Alloy 1 from Table 2. FIG. 1a shows that the grain boundaries of the alloy have substantially low amount of W-bearing phases. FIG. 1b shows gamma prime precipitates in the grain interiors.

FIGS. 2a and 2b show back-scattered electron SEM images of Alloy 2 from Table 2. FIG. 2a shows that the grain boundaries of the alloy are partly covered with W-bearing phases therein. FIG. 2b shows gamma prime precipitates in the grain interiors.

FIGS. 3a and 3b show back-scattered electron SEM images of Alloy 4 from Table 2. FIG. 3a shows that the grain boundaries of the alloy have an increased amount of W-bearing phases therein, compared with Alloy 2. FIG. 3b shows gamma prime precipitates in the grain interiors.

FIGS. 4a and 4b show back-scattered electron SEM images of Alloy 6 from Table 2. FIG. 4a shows that the grain boundaries of the alloy have a higher concentration of fine, discrete W-bearing grain boundary phases therein. FIG. 4b shows gamma prime precipitates in the grain interiors (e.g., greater than 30% by volume).

FIG. 5a shows the grain boundary phase fraction of the alloys of Example 1 discussed herein. As shown, reducing Co content and increasing Fe, W, Ta contents in Alloy 1 led to an increased fraction of W-bearing grain boundary phases in Alloy 2. Further reducing Co content in Alloy 2 increased the fraction of W-bearing grain boundary phases in Alloy 4. An addition of higher boron to Alloy 4 resulted in a higher fraction of W-bearing grain boundary phases in Alloy 6. The “Grain Boundary Phase Fraction” was calculated according to the following method. First, at least (2) backscattered electron (BSE) images were obtained using scanning electron microscopy. Using image analysis software, precipitates containing refractory elements (bright contrast in BSE images) were segmented from other features in the image. Additionally, grain boundaries were segmented from other features in the image while excluding twin boundaries. Grain boundaries thinned to 0.2 μm wide bands were consistently segmented, and the total area fraction of the 0.2 μm wide bands (F_(GB)) was measured. Using an image analysis software, the total area fraction of the refractory element bearing precipitates was measured within the 0.2 μm wide bands (F_(ppT)). The grain boundary phase fraction was measured by dividing F_(PPT) by F_(GB), with the result averaged from multiple images.

FIG. 5b shows the grain boundary phase lineal density of the alloys of Example 1 discussed herein. As shown, Alloy 6 has the highest grain boundary lineal density fraction among the alloys of Example 1. The “Grain Boundary Phase Lineal Density” was calculated according to the following method. First, at least (2) backscattered electron (BSE) images were obtained using scanning electron microscopy. Using image analysis software, precipitates containing refractory elements (bright contrast in BSE images) were segmented from other features in the image. Additionally, grain boundaries were segmented from other features in the image while excluding twin boundaries. Grain boundaries thinned to 0.2 μm wide bands were consistently segmented, and the numbers of grain boundary precipitates were counted in the 0.2 μm wide bands. The grain boundary phase lineal density was calculated by dividing the number of grain boundary precipitates by the total length of the 0.2 μm wide bands, with the results averaged from multiple images.

FIGS. 6a and 6b show the tensile properties of the alloys 1-6 compared to Haynes® Alloy 282 (“HA282”). As the data shows, alloys 1-3 show increasing (i.e., improving) elongation at 1600° F. (i.e., about 871° C.), while the elongation at 1400° F. (i.e., about 760° C.) remains consistently low. Additionally, alloys 3-5 show sufficient elongation at 1600° F. (i.e., about 871° C.) but insufficient elongation at 1400° F. (i.e., about 760° C.). Alloy 6 show sufficient elongation at both 1600° F. and 1400° F. as shown in FIG. 6b . As more particularly shown in FIG. 6a , Alloy 6 has improved 0.2% yield strength at higher temperatures of 1400° F. and 1600° F. (i.e., about 871° C.) compared to HA282.

FIG. 7 shows the creep rupture properties of Alloys 1, 2, 4, 5, and 6 compared to HA282. As shown, Alloys 1, 2 and 6 had about 75° F. (i.e., about 24° C.) higher temperature capability compared with HA282. Alloys 4, and 5 had higher temperature capability compared with HA282, but they are inferior to Alloys 1, 2, and 6.

FIGS. 8a and 8b show the hold time low cycle fatigue (LCF) of the alloys 1-6 measured at 1700° F. (i.e. about 927° C.), in comparison to HA282. At low total strain range (e.g., 0.35%), Alloys 1-3 show increasing (i.e., improving) life. Increased boron contents in Alloys 5 and 6 led to longer hold time LCF life. At high total strain range (e.g., 0.5%), Alloys 3 and 4 do not show significant improvement in hold time LCF life, but Alloys 4 and 6 show increasing (improving) life with the addition of boron.

FIG. 9 shows the fracture toughness (K_(1C)) of Alloys 1, 2, 3, 5, and 6 compared to HA282, as measured at 1700° F. (i.e., about 927° C.). As the data shows, Alloy 1 substantially without grain boundary precipitates shows poor fracture toughness. Alloys 2, 3, 5, and 6 with W-bearing grain boundary precipitates have sufficient K_(1C), while still being lower than HA282.

FIG. 10 shows results of a cyclic oxidation test comparing alloy 6 to HA282 at 1800° F. (i.e., about 982° C.) with cycles of 50 minutes in the furnace and 10 minutes out of the furnace. As shown, the mass change of Alloy 6 is minimal compared with HA282 at 1800° F. (i.e., about 982° C.).

Example 2

The range of boron in the nickel based alloy compositions were explored. Keeping all other concentrations the same, the concentration of boron was changed such that the boron concentration increased from 0.064% by weight to 0.166% by weight. The nickel based alloy compositions shown in Table 3 were prepared, with all values shown in percent by weight (% wt.):

TABLE 3 Exemplary Alloy Compositions % wt. Alloy Co Cr Fe Al W Ta B C Hf Zr Ni A 23.4 10.8 3.9 4.7 11 7.3 0.064 0.05 0.2 0.05 Balance B 23.4 10.8 3.9 4.7 11 7.3 0.083 0.05 0.2 0.05 Balance C 23.4 10.8 3.9 4.7 11 7.3 0.109 0.05 0.2 0.05 Balance D 23.4 10.8 3.9 4.7 11 7.3 0.140 0.05 0.2 0.05 Balance E 23.4 10.8 3.9 4.7 11 7.3 0.149 0.05 0.2 0.05 Balance F 23.4 10.8 3.9 4.7 11 7.3 0.166 0.05 0.2 0.05 Balance

Each of these nickel based alloys was formed into a wrought plate, and their respective microstructures were compared. FIGS. 11a-11f show back-scattered electron SEM images of the alloys A-F, respectively. As shown, alloys A and F showed lower concentration of W-bearing grain boundary phases compared with Alloys B, C, and D. Alloys B, C, and D, exhibited the desired combination of properties, particularly the relatively high amount of W-bearing grain boundary phases along the grain boundaries with fine, discrete forms and the relatively high concentration of gamma prime precipitates in the grain interiors. Alloy E showed slightly less W-bearing grain boundary phases than alloys B, C, and D. The preferred concentration range of boron to form sufficient amount of W-bearing grain boundary phases in fine, discrete morphology was determined to be about 0.065 wt. % to about 0.155 wt. %, preferably about 0.070% by weight to about 0.150% by weight.

FIG. 12a shows the grain boundary phase fraction of the alloys of Example 2 discussed herein. As shown, the grain boundary phase fraction increases with additions of boron to about 1200 ppm, and then decreases with further additions of boron. Sufficient grain boundary phase fraction (e.g., about 20% or greater, such as about 25% or greater) comparable to that of Alloy 6 can be obtained in alloys with boron concentration up to about 0.155 wt %.

FIG. 12b shows the grain boundary phase lineal density of the alloys of Example 2 discussed herein. As shown, similar to the grain boundary phase fraction, the grain boundary phase lineal density increases with additions of boron up to about 1200 ppm, then decreases with further additions of boron. Sufficient grain boundary phase fraction (e.g., about 300/mm or greater, such as about 310/mm or greater) comparable to that of Alloy 6 can be obtained in alloys with boron concentration between about 0.065 wt % and about 0.155 wt %.

While the invention has been described in terms of one or more particular embodiments, it is apparent that other forms could be adopted by one skilled in the art. It is to be understood that the use of “comprising” in conjunction with the alloy compositions described herein specifically discloses and includes the embodiments wherein the alloy compositions “consist essentially of” the named components (i.e., contain the named components and no other components that significantly adversely affect the basic and novel features disclosed), and embodiments wherein the alloy compositions “consist of” the named components (i.e., contain only the named components except for contaminants which are naturally and inevitably present in each of the named components).

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A nickel based alloy, comprising: about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; and the balance nickel.
 2. The nickel based alloy according to claim 1, wherein the nickel based alloy comprises gamma prime precipitates in a plurality of grain interiors and has a gamma prime solvus temperature of about 1038° C. or greater.
 3. The nickel based alloy according to claim 2, wherein the nickel based alloy comprises about 30% by volume or more gamma prime precipitates in the plurality of grain interiors.
 4. The nickel based alloy according to claim 3, wherein the nickel based alloy has a grain boundary phase fraction of about 20% by volume or more.
 5. The nickel based alloy according to claim 4, wherein the nickel based alloy has a grain boundary phase lineal density of about 310 precipitates per mm or greater.
 6. The nickel based alloy according to claim 2, wherein the nickel based alloy comprises precipitates of W-bearing phases along one or more grain boundaries.
 7. The nickel based alloy according to claim 6, wherein the W-bearing phase comprises Laves phase, mu phase, beta phase, sigma phase, borides, or carbides.
 8. The nickel based alloy according to claim 1, wherein the nickel based alloy comprises about 0.065 wt. % to about 0.155 wt. % boron.
 9. The nickel based alloy according to claim 1, wherein the nickel based alloy comprises about 22% by weight to about 24% by weight cobalt, about 10% by weight to about 12% by weight chromium, about 3% by weight to about 5% by weight iron, about 4% by weight to about 5.5% by weight aluminum, about 10% by weight to about 12% by weight tungsten, about 7% by weight to about 8% by weight tantalum, and about 0.07% by weight to about 0.15% by weight boron.
 10. The nickel based alloy according to claim 1, wherein the nickel based alloy further comprises greater than 0% by weight to about 0.1% by weight carbon.
 11. The nickel based alloy according to claim 1, wherein the nickel based alloy further comprises about 0.02% by weight to about 0.08% by weight carbon.
 12. The nickel based alloy according to claim 1, wherein the nickel based alloy further comprises greater than 0% by weight to about 0.5% by weight hafnium.
 13. The nickel based alloy according to claim 1, wherein the nickel based alloy further comprises greater than 0% by weight to about 0.1% by weight zirconium.
 14. A component for a gas turbine assembly comprising the nickel alloy of claim
 1. 15. A nickel based alloy consisting of: about 20 wt. % to about 26 wt. % cobalt; about 9 wt. % to about 13 wt. % chromium; about 2 wt. % to about 6 wt. % iron; about 3.5 wt. % to about 6 wt. % aluminum; about 9 wt. % to about 13 wt. % tungsten; about 6 wt. % to about 9 wt. % tantalum; about 0.06 wt. % to about 0.20 wt. % boron; and the balance nickel.
 16. The nickel based alloy according to claim 15, wherein boron is included in an amount of about 0.065 wt. % to about 0.155 wt. % boron.
 17. The nickel based alloy according to claim 15, consisting of about 22% by weight to about 24% by weight cobalt, about 10% by weight to about 12% by weight chromium, about 3% by weight to about 5% by weight iron, about 4% by weight to about 5.5% by weight aluminum, about 10% by weight to about 12% by weight tungsten, about 7% by weight to about 8% by weight tantalum, and about 0.07% by weight to about 0.15% by weight boron. 